This is a simple work around to the current device stack design. A
ref_count could let different modules to open/close the same device
independently without interfere others in some degree.

But there is still some data shared between the modules, like flag,
open_flag and user_data. Moreover, it won't yield an error if A open a
device, and B read from it before open it in B. Maybe alloc a new handle
in rt_device_open will be the ultimate solution. But that is much bigger
change and we may leave it to future development.

dfs: fix the variable definition bug in copy, found by ffgamelife from rt-thread.org

remove RT_LWIP_TCP_SND_BUF setting

When not configured in rtconfig.h, lwipopt.h will give us a reasonable
value(TCP_MSS * 2).

rm48x50: restore missing include for __TI_COMPILER_VERSION__

Please @Grissiom check why add this header file in rtthread.h.

convert the Tabs to Spaces

convert Tabs to spaces

add logtrace component

Logtrace is a component that could output the log into either a device
or a file. It has the ability to filter the log messages according to a
pre-module level. Define RT_USING_LOGTRACE in rtconfig.h if you want to
have a try.

update libcpu/arm/cortex-m4: support lazy stack optimized.